Complexity–biodiversity relationships on marine urban structures: reintroducing habitat heterogeneity through eco-engineering

Abstract

Urbanization is leading to biodiversity loss through habitat homogenization. The smooth, featureless surfaces of many marine urban structures support ecological communities, often of lower biodiversity, distinct from the complex natural habitats they replace. Eco-engineering (design for ecological co-benefits) seeks to enhance biodiversity and ecological functions on urban structures. We assessed the benefits to biodiversity of retrofitting four types of complex habitat panels to an intertidal seawall at patch (versus flat control panels) and site (versus unmodified control seawalls and reference rocky shores) scales. Two years after installation, patch-scale effects of complex panels on biodiversity ranged from neutral to positive, depending on the protective features they provided, though all but one design (honeycomb) supported unique species. Water-retaining features (rockpools) and crevices, which provided moisture retention and cooling, increased biodiversity and supported algae and invertebrates otherwise absent. At the site scale, biodiversity benefits ranged from neutral at the high- and mid-intertidal to positive at the low-intertidal elevation. The results highlight the importance of matching eco-engineering interventions to the niche of target species, and environmental conditions. While species richness was greatest on rockpool and crevice panels, the unique species supported by other panel designs highlights that to maximize biodiversity, habitat heterogeneity is essential. This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’.

Physical and biogenic complexity mediates ecosystem functions in urban sessile marine communities

“…Again, without manipulating species composition and abundance it is not possible to identify which species is/are contributing to these patterns. Nevertheless, our results re‐enforce the point that there is no one‐size‐fits‐all approach, and interventions should consider the local environment and available species pool (Bishop et al, 2022; Strain et al, 2021). Also, it is important to note that assemblages assessed here were relatively young (7–8 months) and may not represent long term effects of increased physical or biogenic complexity as colonisation of benthic habitats may continue over several years (Butler & Connolly, 1999).…”

Turning a lost reef ecosystem into a national restoration program

“…New funding sources will likely emerge as shellfish reef restoration is increasingly incorporated into other coastal infrastructure projects. For example, opportunities exist to broaden shellfish restoration objectives and activities through alignment with marine eco‐engineering initiatives (e.g., seawalls modified to enhance biodiversity) (Bishop et al., 2022 ), nature‐based solutions to coastal risk reduction (Morris et al., 2021 ), enhancing ecosystem services (nutrient reduction and fisheries enhancement), and aquaculture programs focused on sustainable production (Jones et al., 2022 ). Such alignment could deliver scalable outcomes that benefit multiple partners and investors.…”

Coastal greening of grey infrastructure: an update on the state-of-the-art

“…Based on well-known positive effects of habitat complexity and diversity of refugia on biodiversity across scales, many GGI experiments have focussed on incorporating a variety of small-scale microhabitats to increase the settlement, establishment, and survival of different organisms onto artificial structures. Common strategies include retrofitting human-made infrastructure with concrete tiles molded with topographically complex designs (Perkol-Finkel et al, 2018;Loke et al 2019a;Bishop et al, 2022) or incorporating small-scale complexity into newly built structures (e.g., addition of holes, pits and water-retaining features such as rock pools, Evans et al, 2015;Bender et al, 2020). Early studies enhancing habitat complexity failed to assess the contribution of the increase in surface area (rather than change in complexity) to biodiversity.…”

“…Loke et al (2019b) developed a novel system for testing the independent and interactive effects of habitat area and spatial configuration (i.e., fragmentation pattern) on intertidal species richness and revealed an optimal tile density and spatial configuration to maximize biodiversity on tropical seawalls. Whilst a number of recent studies either use smallscale sampling units (Bishop et al, 2022) or compartmentalize the data by microhabitat (e.g., ridges versus crevices on experimental tiles, Strain et al 2021) in an effort to standardize for surface area, greater attempts to disentangle the effects of increased surface area and addition of topographic complexity is recommended.…”